KR20080089350A - Method for manufacturing soi substrate and soi substrate - Google Patents

Abstract

In a method for manufacturing a SOI substrate by bonding method, a silicon oxide film is formed at least on a single crystal silicon substrate to be a SOI layer or a single crystal silicon substrate to be a supporting substrate, and the single crystal silicon substrate to be the SOI layer and the single crystal silicon substrate to be the supporting substrate are bonded through the silicon oxide film. Then in the case of performing bonding heat treatment to improve bonding strength, at least heat treatment for holding the work at a temperature within a range of 950°C to 1,100°C is performed, and then heat treatment at a temperature higher than 1,100°C is performed. Thus, the SOI substrate manufacturing method by which the SOI substrate having excellent gettering performance against metal contamination of the SOI layer can be efficiently manufactured, and the SOI substrate are provided.

Description

Method for manufacturing SOI substrate and SOI substrate {Method for Manufacturing SOI Substrate and SOI Substrate}

The present invention relates to a method for manufacturing a silicon on insulator (SOI) substrate by a bonding method, and more particularly, to a method for manufacturing a SOI substrate having excellent gettering ability against metal impurities.

One substrate for semiconductor devices is an SOI substrate in which a silicon layer (hereinafter referred to as an SOI layer) is formed on a silicon oxide film as an insulating film.

This SOI substrate has a low parasitic capacitance and high radioactivity since the SOI layer of the substrate surface layer serving as the device fabrication region is electrically separated from the substrate by an embedded oxide film layer (BOX layer). Has the features.

Therefore, high speed, low power consumption operation, soft error prevention, and the like are expected to be expected, which is promising as a substrate for high performance semiconductor devices.

As a manufacturing method of this SOI substrate, the following method is known, for example.

That is, two mirror-polished single crystal silicon substrates (a single crystal silicon substrate (bond wafer) to be a SOI layer and a single crystal silicon substrate (base wafer) to be a support substrate) are prepared, and an oxide film is formed on the surface of at least one silicon substrate. To form.

Then, these single crystal silicon substrates are bonded together with an oxide film therebetween, followed by heat treatment to increase the bonding strength.

Thereafter, the bond wafer is thinned to obtain an SOI substrate on which a silicon on insulator (SOI) layer is formed.

As the method of thinning, there are a method of grinding and polishing the bonded wafer to a desired thickness, a method of peeling the bonded wafer from the ion implantation layer by a method called an ion implantation peeling method, and the like.

As described above, the SOI substrate has many structural merit from the viewpoint of electrical characteristics, but has a structural demerit from the viewpoint of resistance to metal impurity contamination.

That is, in many cases, the diffusion rate of metal impurities is slower in the silicon oxide film than in the silicon.

As a result, when contaminated on the surface of the SOI layer, metal impurities hardly pass through the BOX layer, and thus accumulate in the thin SOI layer.

Therefore, the adverse effect of metal contamination becomes larger than in the case of the silicon substrate which does not have SOI structure.

Therefore, in an SOI substrate, it is one of the more important qualities to have the ability (gettering capability) to trap metal impurities and to remove them from the region which becomes an active layer of a semiconductor element.

In the gettering method (oxygen precipitate, high concentration boron addition, backside polycrystalline silicon film, etc.) generally used in the case of a silicon substrate which does not have an SOI structure, a gettering layer is introduced to the substrate side opposite to the active layer.

However, even when the gettering layer is introduced to the support substrate side using the same technique in the SOI substrate, the gettering layer described above cannot function sufficiently since the metal impurities hardly pass through the BOX layer. There is a problem that it cannot be applied to an SOI substrate.

In order to solve this problem, some methods have been conventionally proposed to introduce a gettering region in the vicinity of the SOI layer of the SOI substrate.

For example, a method of forming a region containing a high concentration of impurities such as phosphorus and boron for gettering in a selective region of the SOI layer is disclosed in Japanese Patent Laid-Open No. 6-163862 or Japanese Patent Laid-Open No. 10-13. 32209 is disclosed.

However, in such a method, there is a problem that the cost is increased and the productivity is lowered by increasing the step of introducing impurities.

In addition, when the impurities introduced for gettering diffuse into the active layer of the semiconductor element by heat treatment in the manufacturing process or the device process of the SOI substrate, adverse effects on the electrical characteristics are feared.

As another method, a method of forming a polycrystalline silicon layer in the area of the SOI layer near the interface between the SOI layer and the BOX layer to getter the metal impurities is disclosed in Japanese Patent Laid-Open No. 6-275525.

However, also in this case, there exists a problem that the process of forming a polycrystalline silicon layer increases, cost increases, and productivity falls.

In addition, when the thickness of the SOI layer is thin, the formation of the polycrystalline silicon layer becomes very difficult.

 SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing an SOI substrate and an SOI substrate capable of efficiently producing an SOI substrate having excellent gettering capability against metal contamination of the SOI layer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and in the method of manufacturing an SOI substrate by a bonding method, a silicon oxide film is formed on at least one surface of a single crystal silicon substrate serving as an SOI layer and a single crystal silicon substrate serving as a support substrate. When the single crystal silicon substrate serving as the SOI layer and the single crystal silicon substrate serving as the support substrate are bonded to each other through the silicon oxide film, a bonding heat treatment for increasing the bonding strength is performed. After the heat treatment maintained at a temperature in the range, a heat treatment at a temperature higher than 1100 ° C. is provided.

As described above, after performing a heat treatment maintained at a temperature in the range of at least 950 ° C. to 1100 ° C., the heat treatment at a temperature higher than 1100 ° C. can add excellent gettering capability to the bonding interface region, SOI substrates having bonding strength can be prepared.

In addition, since no special new process is added, the SOI substrate can be efficiently produced without lowering the productivity and further increasing the cost. Furthermore, since it is unnecessary to form a high concentration layer of impurities, there is no deterioration of other electrical characteristics.

In the method for producing an SOI substrate of the present invention, it is preferable to form the silicon oxide film on the surface of the single crystal silicon substrate serving as the support substrate.

By forming a silicon oxide film on the surface of a single crystal silicon substrate serving as a support substrate, the bonding interface serving as a gettering site becomes an interface between the SOI layer and the BOX layer, so that metal contamination in the SOI layer does not pass through the BOX layer. It is possible to manufacture an SOI substrate that can be gettered without any need.

Moreover, in the manufacturing method of the SOI board | substrate of this invention, it is preferable to make time to hold at the temperature of the said 950 degreeC from 1100 degreeC to 1 hour or more and 4 hours or less.

Thus, by making time to hold 1100 degreeC from 950 degreeC to 1 hour or more and 4 hours or less, sufficient gettering capability can be acquired without reducing productivity.

Moreover, in the manufacturing method of the SOI substrate of this invention, it is preferable that the heat processing which raises the said bond strength includes heat processing in the atmosphere containing water vapor.

As described above, as a heat treatment to increase the bonding strength, after performing a heat treatment that is maintained at a temperature in the range of at least 950 ° C. to 1100 ° C., when performing heat treatment at a temperature higher than 1100 ° C., a heat treatment atmosphere during at least a part of the heat treatment process. If the atmosphere contains water vapor, the gettering capability can be further increased.

In addition, the present invention is an SOI substrate manufactured by the bonding method, which has an SOI layer composed of only single crystal silicon, and in the interface region of the SOI layer and the buried oxide film in the SOI layer, 1 × 10 ¹² atoms / Provided is an SOI substrate having a capability of capturing metal impurities of cm ² or more.

The concentration of metal impurities affecting the electrical properties is 10 ¹¹ atoms / cm ² It is known to be more than one.

Therefore, as long as the gettering capability of 1 × 10 ¹² atoms / cm ² or more is present in the interface region between the SOI layer and the embedded oxide film as in the SOI substrate of the present invention, deterioration of device characteristics due to metal contamination can be sufficiently prevented.

According to the method for producing an SOI substrate according to the present invention, an SOI substrate having excellent gettering capability against metal contamination of the SOI layer can be efficiently produced at low cost.

In addition, the SOI substrate according to the present invention can be a high quality and inexpensive SOI substrate having sufficiently high gettering capability in the SOI layer.

1 is a flow sheet showing the outline of a method for producing an SOI substrate according to a bonding method.

2 is a graph showing an example of the concentration distribution of metal impurities from the surface on the SOI layer side of the SOI substrate to the BOX layer in the experimental example.

Figure 3 is a schematic diagram showing an example of the change pattern of the temperature during the bonding heat treatment of the present invention, (a) is a case where a certain time is maintained at a specific temperature in the heat treatment of the first stage, (b) is a first stage (C) is the case where temperature is changed up and down in the range of 950 degreeC or more and 1100 degreeC or less in the 1st step heat processing, (d) is one step The wafer is once taken out after the second heat treatment, and (e) is a case where the heat treatment furnace is changed.

4 is a graph showing the evaluation results of the gettering capability of the SOI substrate in Example 2. FIG.

5 is a graph showing the evaluation results of the gettering capability of the SOI substrate in Example 3. FIG.

6 is a graph showing the evaluation results of the gettering capability of the SOI substrate in Comparative Example 2. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, although this invention is demonstrated in detail with reference to drawings, this invention is not limited to these.

1 is a flow sheet showing an example of a method for producing an SOI substrate by the bonding method. The outline | summary of the manufacturing method of the SOI substrate by the bonding method to which this invention is applied is as showing below.

First, in step (a), a single crystal silicon substrate (bond wafer) 11 serving as an SOI layer for forming a semiconductor element and a single crystal silicon substrate (base wafer) 12 serving as a support substrate are prepared, and at least one of A silicon oxide film 13 serving as a BOX layer is formed on the surface of the single crystal silicon substrate (here, the oxide film 13 is formed on the base wafer).

Next, in step (b), the single crystal silicon substrate 11 serving as the SOI layer and the single crystal silicon substrate 12 serving as the support substrate are brought into close contact with each other via the silicon oxide film 13.

In this way, the joining wafer 15 having the joining surface 14 is obtained.

Next, in step (c), a bonding heat treatment is performed to increase the bonding strength.

Next, in step (d), the SOI layer is thinned to a desired thickness to obtain an SOI substrate 18 having an SOI layer 16 and a buried oxide film (BOX layer) 17.

In this case, the thinning may be performed by, for example, planar grinding or mirror polishing, and hydrogen or rare gas ions may be applied to the bonding surface of the bond wafer in advance before the step (b) of bonding the bond wafer and the base wafer. An ion implantation peeling method may be used in which an ion implantation layer is formed by implantation, and a thin film is formed by peeling the bond wafer from the ion implantation layer after bonding.

In the case where thinning is performed by ion implantation peeling, after joining at room temperature, if necessary, a low temperature heat treatment of about 500 ° C. is performed to perform peeling, followed by a bonding heat treatment step (c) for increasing bonding strength. Becomes

MEANS TO SOLVE THE PROBLEM In the manufacturing method of the SOI board | substrate by such a joining method, the present inventors add a gettering capability directly to an SOI layer, without adding another special process, such as formation of a high concentration impurity region or formation of a polycrystalline silicon layer. As a result of intensive investigations, it was found that the use of the junction interface itself as a gettering site and the study of bonding heat treatment conditions can add gettering capability to the junction interface region.

That is, the present inventors have found that the heating temperature conditions at the time of joining heat treatment are related to the generation of gettering sites, thereby completing the present invention.

Experimental Example

The present inventors thought that by optimizing the heating temperature during the bonding heat treatment, the gettering capability of the finally produced SOI substrate could be improved, and the following experiments were conducted.

An experimental example will be described with reference to FIG. 1.

First, two mirror-polished N-type single crystal silicon substrates of diameter 200 mm and surface orientation {100} were prepared. On the surface of the single crystal silicon substrate 12 serving as the support substrate, a silicon oxide film 13 having a film thickness of about 1 µm serving as a BOX layer was formed by thermal oxidation (a).

Next, the single crystal silicon substrate 11 serving as the SOI layer and the single crystal silicon substrate 12 serving as the support substrate were bonded to each other with the silicon oxide film 13 interposed therebetween (b).

Next, a bonding heat treatment for increasing the bonding strength was performed under the following conditions (c). That is, the temperature reduction (降溫), and then the wafer after the input of the wafer bonded to a setting heat treatment at 800 ℃ and held for 2 hours to a maximum temperature T was raised to 10 ℃ / min heating rate of up to ₁ ℃, up to 800 ℃ The heat was taken out of the furnace.

T ₁ degreeC was set to 1050 degreeC, 1100 degreeC, 1150 degreeC, and 1200 degreeC, and it did not specifically hold | maintain in elevated temperature.

At this time, as a heat treatment atmosphere during the bonding heat treatment step, the wafer was put at 800 ° C. to 900 ° C. during the temperature rising step, and the dry oxygen atmosphere was used, and the temperature was increased from 900 ° C. to T ₁ ° C. and maintained at T ₁ ° C. for 2 hours. Pyrogenic oxidation (that is, atmosphere containing water vapor) was performed to the middle of the temperature-falling process after that, and it was set as dry oxygen atmosphere until the wafer is taken out at 800 degreeC after that.

Thereafter, the active layer side of the bonded wafer 15 was thinned to a thickness of about 12 µm by planar grinding or mirror polishing to obtain an SOI substrate 18 (d).

The gettering capability of the SOI substrate thus produced was evaluated as follows.

First, Ni was applied to the surface of the SOI layer at a concentration of about 1 × 10 ¹³ atoms / cm ² , and diffused inside by heat treatment at 1000 ° C. for 1 hour.

Next, the surface oxide film, the SOI layer, and the BOX layer were etched in stages, and the Ni concentration in the solution was measured by ICP-MS (inductively coupled plasma mass spectrometry) to measure the depth direction distribution of the Ni concentration.

The surface oxide film and the BOX layer were measured in one step by HF solution, and the SOI layer was divided into six steps in about 2 占 퐉 steps from the surface of the SOI layer.

An example of the measurement result of the depth distribution of Ni concentration is shown in FIG.

This shows that the Ni concentration in the SOI layer in the 10 to 12 µm region, which is an interface region between the Ni-contaminated surface layer and the BOX layer, is high.

In other words, the Ni concentration in the region of 10 to 12 mu m in the SOI layer in FIG. 2 can be regarded as the Ni concentration gettered in the bonding interface region. The evaluation results of the experimental example are shown in Table 1. Ni concentration in Table 1 is Ni concentration gettered to the above-mentioned bonding interface region.

Temperature T ₁ (℃) Ni concentration (atoms / cm ² ) 1050 2.6 × 10 ¹² 1100 1.6 × 10 ¹² 1150 3.9 × 10 ¹¹ 1200 3.7 × 10 ¹¹

From the results in Table 1, it can be seen that the Ni concentration of the bonding interface region is higher at 1050 ° C and 1100 ° C than in the case where the maximum temperature of the bonding heat treatment is 1150 ° C and 1200 ° C.

In other words, it can be seen that when the bonding heat treatment is maintained at 1100 ° C. or lower, more excellent gettering capability is added to the bonding interface region.

From the above results, in the step (c) of FIG. 1, when performing the joining heat treatment to increase the bonding strength, the gettering excellent in the joining interface region is achieved by setting the maximum temperature of the joining heat treatment to 1100 ° C or lower. I could see that I can add the ability.

In addition, although the holding time at the maximum temperature was 2 hours in the experimental example, it is not particularly limited, and the same effect can be obtained even if it is about 1 hour to 4 hours or more if necessary.

The reason why the gettering capability is added to the bonding interface region in the case where the heat treatment is lowered as mentioned above is not clear. However, the bonding state of the bonding interface or any defects caused by it become the gettering site. I think that. When the heating temperature is higher than 1100 ° C., it is considered that a defect having a higher integrity is formed and a gettering site is not formed or disappears.

From the results of the experimental example, it was found that by performing the bonding heat treatment at a temperature of 1100 ° C. or less, excellent gettering capability can be added to the bonding interface region.

However, SOI substrates subjected to bond heat treatment at a temperature of 1100 ° C. or lower, particularly 1050 ° C. or lower, have a weaker bond strength than SOI substrates subjected to bond heat treatment at a temperature higher than 1100 ° C. There is a possibility of causing a decrease in yield due to peeling of the SOI layer or the like.

Therefore, the present inventors conducted intensive investigation and examination in order to find a method for obtaining higher bonding strength while maintaining excellent gettering capability in the above-described bonding interface region.

As a result, it was found that by performing the heat treatment at a low temperature of 1100 ° C. or lower as described above, the heat treatment at a higher temperature can provide a firm bonding force and control the generation of gettering sites.

Specifically, in the method of manufacturing an SOI substrate as shown in FIG. 1, when the heat treatment in the following two steps is performed in the bonding heat treatment of FIG. 1 (c), excellent gettering capability and high bond strength are obtained. Can be obtained.

That is, the heat treatment in the first stage is a heat treatment maintained at a temperature in the range of at least 950 ° C. to 1100 ° C., and the heat treatment in the second step is heat treatment at a temperature higher than 1100 ° C. and below the melting point of silicon.

Although the holding time of the heat processing of a 1st step is not specifically limited, For example, it can be made into 1 hour or more and 4 hours or less. If it is shorter than 1 hour, sufficient gettering capability may not be obtained.

Moreover, if it is longer than 4 hours, productivity will fall. The holding time of the second heat treatment is not particularly limited, and may be appropriately selected.

In addition, said "keeping at the temperature of the range of at least 950 degreeC to 1100 degreeC" normally means to hold | maintain for a predetermined time at specific temperature (constant temperature) of the range of 950 degreeC to 1100 degreeC, but this invention It is not limited only to this.

That is, what is necessary is just to keep the range of 950 degreeC or more and 1100 degrees C or less, and if it is the range which can acquire the effect of this invention, it shall also include these.

For example, it is a following pattern and the schematic graph was shown in FIG.

That is, the method (a) for maintaining a constant time at a specific temperature in the range of 950 ° C to 1100 ° C, and the temperature increase rate in the range of 950 ° C to 1100 ° C from a wafer input temperature to 950 ° C (eg For example, the method (b) of using a lower sustained temperature (for example, less than 10 ° C / minute) compared to 10 ° C / minute or more and 30 ° C / minute or less), and changing the temperature up and down in the range of 950 ° C or more and 1100 ° C or less The same method (c) or the like, or a combination thereof.

However, considering productivity and cost, the method (a) or (b) is preferable.

In addition, as shown in (d), the wafer may be taken out after the first heat treatment and then cleaned, and then the second heat treatment may be performed, and as shown in (e), the heat treatment furnace may be changed. Thus, after the first stage of heating, it may be cooled once, and then the second stage of heat treatment may be performed in another heat treatment furnace.

In this case, the second heat treatment may be performed by RTA (Rapid Thermal Anealing).

Even in the method of performing the above-described bonding heat treatment in two steps, the detailed reason why the gettering capability is added is not clear, but the holding interface is maintained at a temperature in the range of 950 ° C. to 1100 ° C. in the first step to give a bonding interface. Any defect that becomes a turing site is formed, and if it is a gettering site formed by holding in this temperature range, it is thought that this defect does not disappear but remains stable even in heat treatment at the temperature higher than 1100 degreeC of a 2nd step. do.

According to the above method, the gettering layer can be introduced into the SOI substrate while maintaining a high bond strength without adding a special new process such as introduction of high purity impurities.

That is, since no special new process is added, an SOI substrate having a high gettering ability can be efficiently produced without lowering productivity and further increasing the cost.

Moreover, according to the present invention, there is no adverse effect on the element formation region by thermal diffusion of impurities such as phosphorus and boron which are problematic in the method of introducing impurities such as phosphorus and boron to form a gettering layer.

Moreover, this invention is suitable also when the thickness of an SOI layer is thin and it is difficult to introduce a gettering layer by forming a polycrystalline silicon layer in the interface of SOI layer and BOX layer.

In the above embodiment, planar grinding and mirror polishing are performed as a step of thinning the bond wafer after bonding, but instead of these, hydrogen ions or rare gas ions are injected into the surface layer of the bond wafer before bonding to form an ion implantation layer. In addition, a method called an ion implantation peeling method may be used in which the surface and the surface of the base wafer are bonded through an oxide film and heat-treated at a low temperature of about 500 ° C. to be separated from the ion implantation layer to form an SOI layer.

In this case, a method of peeling from the ion implantation layer by mechanical stress may be used without performing heat treatment at about 500 ° C. by performing plasma treatment on the bonded wafer surface and then bonding them together. have.

In either case, since the bonding strength of the bonding interface of the SOI wafer immediately after peeling is insufficient to be introduced into the device process, it is necessary to add heat treatment to increase the bonding strength.

By applying the heat treatment of the present invention as the heat treatment at this time, an SOI wafer having excellent gettering ability of the bonding interface region can be produced, and therefore the present invention is particularly suitable when the thinning is performed by an ion implantation peeling method.

By the way, in this invention, a gettering layer is formed in the vicinity of the joining surface of the single crystal silicon substrate used as an SOI layer, and the single crystal silicon substrate used as a support substrate.

In other words, when the silicon oxide film is formed on the surface of the single crystal silicon substrate serving as the support substrate, the silicon oxide film is formed on the surface of the single crystal silicon substrate serving as the SOI layer when the silicon oxide film is formed on the interface region between the BOX layer and the SOI layer. The gettering layer is formed in the interface region with the BOX layer.

At this time, since the bonding state of the bonding surface does not differ in both, the gettering capability of both gettering layers is equal.

However, due to the difference between the diffusion rate in silicon and the diffusion rate in silicon oxide of metal impurities, the metal impurities are difficult to pass through the BOX layer. Therefore, in order to getter metal contamination adhered to the surface of the SOI layer serving as the device fabrication region, the gettering layer is preferably formed in the interface region between the BOX layer and the SOI layer.

In other words, it is better to form a silicon oxide film on the surface of the single crystal silicon substrate serving as the support substrate and perform bonding.

However, even when the silicon oxide film is formed on the surface of the single crystal silicon substrate serving as the SOI layer, and the gettering layer is formed at the interface region between the support substrate and the BOX layer, it is larger than when the gettering layer is introduced on the backside of the SOI substrate. Turing ability is obtained.

In addition, the thickness of the BOX layer of an SOI substrate is made thin every year.

If the thickness of the BOX layer is thin, for example 100 nm or less, even a gettering layer formed in the interface region between the support substrate and the BOX layer is effective for gettering of metal contamination in the SOI layer.

According to the manufacturing method of the SOI substrate by the bonding method as described above, it has a SOI layer composed of single crystal silicon only, and in the interface region between the SOI layer and the buried oxide film in the SOI layer, 1 × 10 ¹² atoms / cm SOI substrates can be produced that have the ability to capture ^two or more metallic impurities.

It is known that the concentration of metal impurities affecting the electrical properties is 10 ¹¹ atoms / cm ² or more.

Thus, the present invention has a gettering capability of 1 × 10 ¹¹ atoms / cm ² or more, in particular, 1 × 10 ¹² atoms / cm ² If the above gettering capability is in the interface region between the SOI layer and the buried oxide film, deterioration of device characteristics due to metal contamination in the element formation region in the SOI layer can be effectively prevented.

In addition, an SOI substrate having an SOI layer composed of only single crystal silicon and having a gettering layer in the SOI layer is excellent in electrical characteristics and does not adversely affect the device, so that the SOI layer and the BOX layer are near the interface. It is not obtained by the method of forming a high concentration impurity layer, a polycrystalline silicon layer, or the like in the SOI layer region.

Hereinafter, although an Example of this invention is given and this invention is demonstrated more concretely, this invention is not limited to these.

(Example 1)

Based on the process shown in FIG. 1, the SOI substrate was produced as follows.

First, as in the experimental example, two mirror-polished N-type single crystal silicon substrates of diameter 200 mm and surface orientation {100} were prepared.

On the surface of the single crystal silicon substrate 12 serving as the support substrate, a silicon oxide film 13 having a film thickness of about 1 µm serving as a BOX layer was formed by thermal oxidation (a).

Next, the single crystal silicon substrate 11 serving as the SOI layer and the single crystal silicon substrate 12 serving as the support substrate were bonded to each other so as to sandwich the silicon oxide film 13 therebetween (b).

Next, a bonding heat treatment was performed to increase the bonding strength (c).

After In the bonded wafer in which a heat treatment furnace maintained at 800 ℃, and the temperature is raised to the holding temperature of T ₂ ℃ to 10 ℃ / min was maintained for 2 hours at a temperature rising rate of T ₂ ℃.

Then, after heating up to 1150 degreeC which is the maximum temperature, and hold | maintaining for 2 hours, after temperature-falling to 800 degreeC, the wafer was taken out of the furnace.

T ₂ ℃ was set to 950 ℃, 1000 ℃, 1100 ℃ .

At this time, as the heat treatment atmosphere during the bonding heat treatment step, a temperature of the dry oxygen atmosphere is increased from T ₂ ° C. to 1150 ° C. and 1150 between the wafer input at 800 ° C. and the temperature increase step from T ₂ ° C. to 2 hours holding. Pyrogenic oxidation (that is, atmosphere containing water vapor) was performed until hold | maintenance at 2 degreeC after hold | maintaining at 2 degreeC, and it was made into the dry oxygen atmosphere until taking out a wafer at 800 degreeC after that.

Thereafter, the active layer side of the bonded wafer 15 was thinned to a thickness of about 12 µm by planar grinding or mirror polishing to obtain an SOI substrate 18 (d).

The gettering capability of the SOI substrate thus produced was evaluated by the same method as in the experimental example.

(Comparative Example 1)

In the manufacturing procedure of the SOI substrate of Example 1, the SOI substrate was produced when the holding temperature T ₂ ° C in the temperature rising process of the bonding heat treatment was 900 ° C and 1125 ° C.

In addition, the gettering ability was evaluated by the same method as the experimental example.

The evaluation results of the gettering capability of Example 1 and Comparative Example 1 are shown in Table 2.

Holding temperature T ₂ (℃) Ni concentration (atoms / cm ² ) 900 3.9 × 10 ¹¹ 950 2.1 × 10 ¹² 1000 3.0 × 10 ¹² 1100 1.5 × 10 ¹² 1125 6.8 × 10 ¹¹

As shown in Table 2, the case where the holding temperature T ₂ ° C in the temperature increase process of the bonding heat treatment is 950 to 1100 ° C of Example 1, compared to the 900 ° C, 1125 ° C of Comparative Example 1, It turns out that Ni concentration is high.

That is, even when the maximum temperature is 1150 ° C or higher, it can be seen that when the temperature is maintained at a temperature in the range of 950 to 1100 ° C, better gettering capability is added to the bonding interface region.

Moreover, it has sufficient ability to getter Ni of 1 * 10 <^12> atoms / cm <^2> or more.

In addition, although the SOI board | substrate produced by Example 1 and the comparative example 1 was thrown into the normal device process, peeling etc. did not occur and there was no problem in bond strength.

As mentioned above, according to this invention, it turned out that the SOI board | substrate which has the excellent gettering capability can be manufactured efficiently.

(Examples 2 and 3)

Based on the process shown in FIG. 1, the SOI substrate was produced as follows.

First, two N-type silicon single crystal substrates were prepared in the same manner as in Example 1, and a silicon oxide film 13 having a film thickness of about 1.3 mu m serving as a BOX layer was opened on the surface of the single crystal silicon substrate 12 serving as a support substrate. Formed by oxidation (a).

Next, the single crystal silicon substrate 11 serving as the SOI layer and the single crystal silicon substrate 12 serving as the support substrate were bonded to each other with the silicon oxide film 13 interposed therebetween (b). Subsequently, the bonded wafer was placed in a heat treatment furnace maintained at 800 ° C., and the temperature was raised to 1000 ° C., which is a holding temperature at a temperature rising rate of 10 ° C./min, and maintained for 2 hours. Then, the temperature was raised to 1150 ° C. and maintained for 2 hours. Then, after cooling to 800 degreeC, the wafer was taken out of the furnace.

At this time, as the heat treatment atmosphere during the bonding heat treatment step, the wafer was put at 800 ° C. to 900 ° C. during the temperature rising step, and the dry oxygen atmosphere was used. Pyrogenic oxidation (i.e., atmosphere containing water vapor) is carried out through the step of raising the temperature to 1150 ° C. and each step of holding at 1150 ° C. for 2 hours until the strong temperature, and then drying the wafer at 800 ° C. until the wafer is taken out. Two types were used: an oxygen atmosphere (Example 2) and all the heat treatment atmospheres in the combined heat treatment step were a dry oxygen atmosphere (Example 3).

The gettering capability of the SOI substrate thus produced was evaluated in the same manner as in FIG. 2 of the experimental example, and is shown in FIGS. 4 (Example 2) and 5 (Example 3).

 (Comparative Example 2)

In the fabrication procedure of the SOI substrate of Example 3, an SOI substrate was produced in the case where only the heat treatment was performed at 1150 ° C. for 2 hours without holding at 1000 ° C. for 2 hours as the bonding heat treatment, and the same method as in Example 3 was performed. It evaluated as shown in FIG.

From the result of Example 2, 3 and the comparative example 2, the following can be said.

When combined heat treatment is performed in an atmosphere containing water vapor as in Example 2, Ni gettered near the interface between the SOI layer and the BOX layer, as compared with the case where heat treatment is performed in an atmosphere not containing water vapor as in Example 3 The density | concentration shows the high value of 1 or more digits, and it turns out that it has the more excellent gettering ability.

As described above, the reason why the gettering capability is not increased when combined heat treatment is performed in an atmosphere containing water vapor is not clear. However, the presence of water molecules having a smaller molecular radius than that of oxygen molecules causes formation of defects near the interface. It seems to be involved in maintenance.

On the other hand, even when the heat treatment is performed in an atmosphere not containing water vapor as in Example 3, when the combined heat treatment is performed by the heat treatment method according to the middle holding of the present invention, compared with the heat treatment method not following the middle holding as in Comparative Example 2 In other words, the Ni concentration gettered near the interface between the SOI layer and the BOX layer shows a high order of one digit, indicating that the gettering capability is obtained.

Therefore, in order to obtain higher gettering capability, it is preferable to perform the combined heat treatment of the present invention in an atmosphere containing water vapor.

However, since the atmosphere containing water vapor has a high oxidation rate, for example, when applied to a thin film SOI wafer fabricated using an ion implantation peeling method, the amount of reduction in the film thickness of the SOI layer becomes large, and the desired SOI layer is desired. The thickness may not be obtained.

As described above, when it is difficult to use an atmosphere containing water vapor, it is effective to perform the combined heat treatment of the present invention in an atmosphere not containing water vapor.

In addition, this invention is not limited to the said embodiment. The said embodiment is a mere illustration, Comprising: It has the structure substantially the same as the technical idea described in the claim of this invention, and exhibits the same effect, any thing is contained in the technical scope of this invention.

For example, in the above embodiment, the surface of the bonded wafer is subjected to planar grinding or mirror polishing as a step of thinning the bonded wafer, but instead, the bonded wafer is thinned using a method called ion implantation peeling. Also good.

In addition, as long as the temperature hold | maintained in the heating of the 1st step at the time of bonding heat processing is maintained at least 950 degreeC or more and 1100 degrees C or less, you may change with time over time in the temperature range.

Claims (5)

In the method for producing an SOI substrate by the bonding method, at least one silicon oxide film is formed on one surface of a single crystal silicon substrate serving as an SOI layer and a single crystal silicon substrate serving as a supporting substrate, and the SOI layer is formed through the silicon oxide film. After joining the single crystal silicon substrate to be the support substrate and the single crystal silicon substrate to be the supporting substrate, and performing a bond heat treatment to increase the bonding strength, after performing a heat treatment to be maintained at a temperature in the range of at least 950 ° C. to 1100 ° C., the temperature is 1100 ° C. A method for producing an SOI substrate, characterized by performing a higher temperature heat treatment. The method of manufacturing an SOI substrate according to claim 1, wherein the silicon oxide film is formed on a surface of a single crystal silicon substrate serving as the support substrate. The method for manufacturing an SOI substrate according to claim 1 or 2, wherein the time for holding at a temperature in the range of 950 ° C to 1100 ° C is 1 hour or more and 4 hours or less. The method for manufacturing an SOI substrate according to any one of claims 1 to 3, wherein the heat treatment to increase the bonding strength includes heat treatment in an atmosphere containing water vapor. An SOI substrate produced by the bonding method, which has an SOI layer composed of only single crystal silicon, and at least 1 × 10 ¹² atoms / cm ² or more of metal impurities in the interface region between the SOI layer and embedded oxide film in the SOI layer SOI substrate having the ability to capture.

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